Neural scaffolds

ABSTRACT

Disclosed herein are compositions and methods useful for preparing neural scaffolds. The scaffolds comprise tissue taken from the spinal cord and/or dura mater of vertebrate and can be processed to form gels or sheets. Methods of treating patient with CNS injury are also presented.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 12/718,227, filed Mar. 5, 2010, issued as U.S. Pat. No.8,685,634, which claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/157,999, filed Mar. 6, 2009, both of which areincorporated herein in their entirety.

STATEMENT REGARDING FEDERAL FUNDING

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms as provided for by the terms of Grant No.5T32EB000424-05 awarded by the National Institutes of Health.

BACKGROUND OF THE INVENTION

To date, no biocompatible scaffold has successfully engrafted withneural tissue. Thus, there is a significant clinical need for a methodto support axonal sparing, remodeling and tissue regeneration within aninjured spinal cord.

SUMMARY

Tissue scaffolds for neural tissue regeneration and replacement aredisclosed herein. In certain embodiments, scaffolds are derived fromspinal cord tissue that has been decellularized. Such decellularizedneural scaffolds can be manufactured using enzymatic and chemicaltreatment protocols, for example, to remove cellular and extracellularmaterials from spinal cord tissue. In certain embodiments, the neuralscaffolds are at least partially in a gel state. The gel properties ofsuch scaffolds allow direct placement or injection into tissues,including the brain and spinal cord, to create a local niche/environmentconducive to regeneration. According to certain embodiments, thescaffolds are biodegradable, elastomeric, porous and biocompatible.

In certain embodiments, neural scaffolds can be lyophilized for storage.In yet other embodiments, the scaffolds can be used as a sheet or madeinto a powder. In certain other embodiments, dehydrated neural scaffoldscan be reconstituted as either a solution or a gel for use. In variousembodiments, neural scaffolds can be sterilized using irradiation,ethylene oxide, or other methods.

In yet other embodiments, neural scaffolds can also be chemicallymodified to act as a drug delivery system at a site of neural injury ordisease.

Neural scaffold are particularly useful for inducing, supporting, andguiding the growth of neuronal cells into sites of neural disease orinjury, such as in the central nervous system (CNS) and spinal cord. Forexample in one embodiment, a neural scaffold is grafted at, around ornear a site in need of wound healing, tissue remodeling and/or tissueregeneration. In another non-limiting embodiment, such a scaffoldcomprises cells. For example and without limitation, such a methodcomprises culturing cells in and/or on a biodegradable elastomericscaffold in vitro and implanting the scaffold. In yet anothernon-limiting embodiment, the biodegradable elastomeric scaffoldcomprises bioactive or therapeutic agents, such as, without limitationgrowth factors, antibiotics, and anti-inflammatory agents. For example,in certain embodiments, neural scaffolds can be seeded withstem/progenitor cells and/or ensheathing glia (such as olfactoryensheathing glia, oligodendrocyte lineage cells and Schwann cells).

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The preferred embodiments of the present invention, illustrative of thebest mode in which applicant has contemplated applying the principles,are set forth in the following description and are shown in thedrawings, and are particularly and distinctly pointed out and set forthin the appended claims.

FIG. 1 is a digital image showing the gel-like quality of the spinalcord parenchyma-derived scaffold. The thick arrow indicates the gel-likesubstance and the thin arrow indicates the pia matter (6×);

FIGS. 2A-B are fluorescence photomicrographs of the acellular spinalcord parenchyma-derived scaffold showing lack of nuclei and cells withinthe scaffold, which has been stained with nuclei marker DAPI (200×);

FIG. 3 is a photomicrograph of Masson's trichome stained acellularspinal cord parenchyma-derived scaffold (200×);

FIG. 4A-4D are photomicrographs of acellular spinal cordparenchyma-derived scaffold. FIG. 4A shows hematoxylin and eosin (H&E)stained acellular porcine spinal cord-derived scaffold (100×). FIG. 4Bshows Masson's trichrome stained acellular porcine spinal cord-derivedscaffold (100×). FIG. 4C shows Masson's trichrome stained normal adultporcine spinal cord, grey matter (100×). FIG. 4D shows Masson'strichrome stained normal adult porcine spinal cord, white matter (100×);

FIG. 5A-5B are scanning electron micrographs of acellular spinal cordparenchyma-derived scaffold. FIG. 5A shows the scaffold at 600×magnification and FIG. 5B shows the scaffold at 2,000× magnification;

FIGS. 6A-6C are photomicrographs of Masson's trichrome stained acellularspinal cord parenchyma-derived scaffold implanted with neuronal cells(PC12). FIGS. 6A-6C show neuronal cell growth and migration into thescaffold, where neuronal cells (red, thin arrows) grow on and into thescaffold (blue, thick arrows). Photomicrographs are shown at thefollowing magnifications: 100× (FIG. 6A), 200× (FIG. 6B), and 400× (FIG.6C);

FIGS. 7A-7B are photomicrographs of Masson's trichrome stained acellularspinal cord parenchyma-derived scaffold implanted with neuronal cells(PC12). FIGS. 7A-7B show neuronal cell growth and migration into thescaffold (blue, thick arrows), where neuronal cells grow on the surfaceof the scaffold (red, thin arrows) and migration into the scaffold(arrowheads). Photomicrographs are shown at the followingmagnifications: 200× (FIG. 7A) and 400× (FIG. 7B); and

FIGS. 8A-8D are photomicrographs of acellular dura mater-derivedscaffold. FIG. 8A shows a fluorescence photomicrograph of the acellulardura mater scaffold showing lack of nuclei and cells within thescaffold, which has been stained with nuclei marker DAPI (200×). FIG. 8Bshows Masson's trichrome stained acellular porcine dura mater scaffold(100×). FIGS. 8C-8D show Masson's trichrome stained photomicrographs ofneuronal cell growth (red) on the acellular dura mater scaffold (blue);photomicrograph magnification: 200× (FIG. 8C) and 400× (FIG. 8D).

Similar numerals refer to similar parts throughout the drawings.

DETAILED DESCRIPTION OF THE INVENTION

Described herein are scaffolds suitable for use in tissue engineeringand regenerative medicine applications, such as replacement of neuraltissue. In certain embodiments, the scaffold comprises decellularizedspinal cord tissue. Such tissue can be in a gel state. In anothernon-limiting embodiment, the scaffold comprises bioactive or therapeuticagents.

The use of numerical values in the various ranges specified in thisapplication, unless expressly indicated otherwise, are stated asapproximations as though the minimum and maximum values within thestated ranges are both preceded by the word “about”. In this manner,slight variations above and below the stated ranges can be used toachieve substantially the same results as values within the ranges.Also, unless indicated otherwise, the disclosure of these ranges isintended as a continuous range including every value between the minimumand maximum values. For definitions provided herein, those definitionsrefer to word forms, cognates and grammatical variants of those words orphrases.

Scaffolds can be used for a large number of medical applicationsincluding, but not limited to, wound healing, tissue remodeling, andtissue regeneration. For example and without limitation, such scaffoldscan be used for wound healing. In one non-limiting embodiment, thescaffold comprises bioactive agents to facilitate tissue healing, tissueremodeling and/or angiogenesis. In another non-limiting embodiment, thescaffold comprises bioactive agents to ward off bacteria and otherpathogens. In yet another non-limiting embodiment, the scaffoldcomprises pores to allow a wound to drain. In yet another non-limitingembodiment, the scaffold comprises combinations of cells and bioactiveagents. In another non-limiting embodiment, combinations of cells andbioactive agents are added to the scaffold before or during implantationat a site in a patient.

As used herein, the term “polymer” refers to both synthetic polymericcomponents and biological polymeric components. The scaffolds describedherein can comprise any suitable combination of synthetic polymericcomponents and biological polymeric components. “Biological polymer(s)”are polymers that can be obtained from biological sources, such as,without limitation, mammalian or vertebrate tissue, as in the case ofcertain extracellular matrix-derived (ECM-derived) compositions. As usedherein the term “extracellular matrix” refers to any polymer remainingafter decellularization including gels and solids. Biological polymerscan be modified by additional processing steps. Polymer(s), in generalinclude, for example and without limitation, mono-polymer(s),copolymer(s), polymeric blend(s), block polymer(s), block copolymer(s),cross-linked polymer(s), non-cross-linked polymer(s), linear-,branched-, comb-, star-, and/or dendrite-shaped polymer(s), wherepolymer(s) can be formed into any useful form, for example and withoutlimitation, a hydrogel, a porous mesh, a fiber, woven mesh, or non-wovenmesh, such as, for example and without limitation, a non-woven meshformed by electrodeposition.

Generally, the polymeric components suitable for the scaffold describedherein may be any polymer that is biodegradable and biocompatible. By“biodegradable”, it is meant that a polymer, once implanted and placedin contact with bodily fluids and/or tissues, will degrade eitherpartially or completely through chemical, biochemical and/or enzymaticprocesses. Non-limiting examples of such chemical reactions includeacid/base reactions, hydrolysis reactions, and enzymatic cleavage.

In certain non-limiting embodiments, the biodegradable polymers maycomprise homopolymers, copolymers, and/or polymeric blends comprising,without limitation, one or more of the following monomers: glycolide,lactide, caprolactone, dioxanone, and trimethylene carbonate. In othernon-limiting embodiments, the polymer(s) comprise labile chemicalmoieties, non-limiting examples of which include esters, anhydrides,polyanhydrides, or amides, which can be useful in, for example andwithout limitation, controlling the degradation rate of the scaffoldand/or the release rate of therapeutic agents from the scaffold.Alternatively, the polymer(s) may contain peptides or biomacromoleculesas building blocks which are susceptible to chemical reactions onceplaced in situ. In one non-limiting example, the polymer is apolypeptide comprising the amino acid sequence alanine-alanine-lysine,which confers enzymatic lability to the polymer. In another non-limitingembodiment, the polymer composition may comprise a biomacromolecularcomponent derived from an ECM. For example, the polymer composition maycomprise the biomacromolecule collagen so that collagenase, which ispresent in situ, can degrade the collagen.

The polymer components may be selected so that they degrade in situ on atimescale that is similar to an expected rate of healing of the wound ortissue. Non-limiting examples of in situ degradation rates includebetween one week and one year or increments therebetween for instance,between two weeks and 10 months, and between one month and six month.

The polymeric components used to make the devices disclosed herein arepreferably biocompatible. By “biocompatible,” it is meant that a polymercomposition and its normal degradation in vivo products arecytocompatible and are substantially non-toxic and non-carcinogenic in apatient within useful, practical and/or acceptable tolerances. By“cytocompatible,” it is meant that the polymer can sustain a populationof cells and/or the polymer composition, device, and degradationproducts, thereof are not cytotoxic and/or carcinogenic within useful,practical and/or acceptable tolerances. For example, the polymer whenplaced in a human cell culture does not adversely affect the viability,growth, adhesion, and number of cells. In one non-limiting embodiment,the compositions, and/or devices are “biocompatible” to the extent theyare acceptable for use in a human patient according to applicableregulatory standards in a given jurisdiction. In another example thebiocompatible polymer, when implanted in a patient, does not causesubstantial adverse reaction or substantial harm to cells and tissues inthe body, for instance, the polymer composition or device does not causenecrosis or an infection resulting in harm to tissues from the implantedscaffold.

The mechanical properties of a biodegradable elastomeric scaffold can beoptimized to operate under the normal strain and stress on the nativetissue at the site of implantation. In certain non-limiting embodiments,the mechanical properties of the scaffold are optimized similar to oridentical to that of native tissue,

The mechanical properties of the scaffold also may be optimized to besuitable for surgical handling. In certain embodiments the scaffold is agel and has gel like properties that can be controlled by the degree ofhydration. For example, the gel can be a hydrogel and be semi-solid,thus having a three dimensional structure. In another non-limitingembodiment, the scaffold is a flexible sheet and can be sutured to thesite. In another, the scaffold is foldable and can be delivered to thesite by minimally invasive laparoscopic methods.

Variables that can be optimized include without limitation, the extentof physical cross-linking in a network comprising polymeric components,the ratio of polymeric components within the network, the distributionof molecular weight of the polymeric components, and the method ofprocessing the polymers. Polymers are typically semicrystalline andtheir physical properties and/or morphology are dependent upon a largenumber of factors, including monomer composition, polydispersity,average molecular weight, cross-linking, and melting/crystallizationconditions. For example, flow and/or shear conditions during cooling ofa polymer melt are known to affect formation of crystalline structuresin the composition. In one non-limiting embodiment, the scaffoldcomprises a polymeric component that provides strength and durability tothe scaffold, yet is elastomeric so that the mechanical properties ofthe scaffold are similar to the native tissue surrounding the wound orsite in need of tissue regeneration.

The extracellular matrix is useful for promoting cell growth on theelastomeric scaffold, extracting appropriate host cells forconstruction, remodeling, and/or enhancement of biocompatibility. In onenon-limiting embodiment, the biological polymeric component comprisesand includes an extracellular matrix-derived material. As used herein,the terms “extracellular matrix” and “ECM” refer to a complex mixture ofstructural and functional biomolecules and/or biomacromoleculesincluding, but not limited to, structural proteins, specializedproteins, proteoglycans, glycosaminoglycans, and growth factors thatsurround and support cells within mammalian tissues. By “ECM-derivedmaterial” it is meant a composition that is prepared from a natural ECMor from an in vitro source wherein the ECM is produced by cultured cellsand comprises one or more polymeric components (constituents) of nativeECM. Additionally, “decellularized” ECM refers to ECM in which the cellshave been removed through processes described herein and known in theart.

According to one non-limiting example of the ECM-derived material, ECMis isolated from a vertebrate animal, for example, from a warm bloodedmammalian vertebrate animal including, but not limited to, human,monkey, pig, cow, sheep, etc. In one non-limiting embodiment, the ECM isisolated from spinal cord, which may or may not include the dura mater.In another non-limiting embodiment, the ECM includes at least a portionof the dura mater. In certain non-limiting embodiments, the materialthat serves as the biological component of the scaffold consistsprimarily (e.g., greater than 70%, 80%, or 90%) of ECM. In anothernon-limiting embodiment, the biodegradable elastomeric scaffold maycontain at least 50% ECM, at least 60% ECM, at least 70% ECM, and atleast 80% ECM. In yet another non-limiting embodiment, the biodegradableelastomeric scaffold comprises at least 10% ECM. The ECM material may ormay not retain some of the cellular elements that comprised the originaltissue. The type of ECM used in the scaffold can vary depending on theintended cell types to be recruited during wound healing or tissueregeneration, the native tissue architecture of the tissue organ to bereplaced, the availability of the tissue source of ECM, or other factorsthat affect the quality of the final scaffold and the possibility ofmanufacturing the scaffold. For example and without limitation, the ECMmay contain both a basement membrane surface and a non-basement membranesurface, which would be useful for promoting the reconstruction oftissue. In certain embodiments, an implantable device can compriseeither a smooth basement membrane surface (luminal) or a roughnon-basement surface (abluminal).

In one non-limiting embodiment, neural scaffolds are made by firstremoving the cells from excised CNS tissue and then removing anyremaining lipids and DNA. Notably, excised CNS tissue is ensheathed inthe dura mater membrane. The membrane can be removed and processedindependently of the neural tissue according to the methods disclosed.As a result of the processing methods disclosed herein, a gel can bemade from cellular spinal cord material; whereas, processing ofacellular dura mater creates a fibrous sheet. Those of ordinary skill inthe art recognize that washing steps may be performed at any time in theprocedures disclosed herein without substantially changing thecomposition or function of the tissue.

In certain embodiments the decellularization process comprisesincubating the tissue (whether the dura mater, spinal cord parenchymaltissue, or a combination thereof) in a solution of non-ionic detergent.Non-ionic detergents are capable of lysing cells and solubilizing thecell membrane as well as many of the cellular components. It iscontemplated that various detergents can be used. For example, incertain embodiments, TRITON X100™ (4-octylphenol polyethoxylate) can beused. However, the methods disclosed herein may be adapted to use anyother octylphenol polyethoxylate as well as other detergents such asn-dodecylmaltoside, NONIDET P40™, n-octylglucoside, TWEEN 20, andothers.

In certain embodiments, the tissue is placed into a cassette. The term“cassette” is intended to mean any three-dimensional hollow structure inwhich tissue can be place into for processing, such as a tissue cassetteor other similar device. As the processed spinal cord parenchymal tissueis a gel, such a cassette helps maintain the tissue structure as well assimplifies handling procedures.

In some embodiments, the neural tissue can be pre-processed. Forexample, in one embodiment, the tissue is digested using trypsin-EDTA, aprotease, before the decellularization process begins. Those of skill inthe art recognize that incubation times and temperatures can be varieddepending on the amount of tissue. Thus, in certain embodiments, tissuecan be digested for 30 minutes at 37° C.

For the decellularization process, tissue can be processed in anon-ionic detergent such as described herein. For example, in oneembodiment the tissue can be placed in increasing amounts of TRITONX100™ solutions. In one embodiment, the tissue can be incubated in3-6%-9%, TRITON X100™ solutions for periods up to 48-72 hours for eachpercentage. In certain embodiments, the incubation is performed at 4° C.The solutions may be changed as often as needed based on monitoring ofthe cell cellular removal process.

To remove lipids from the scaffold, an emulsifier can be used. Forexample, in certain embodiments, lecithin or lecithin-deoxycholate, canbe used, although any suitable emulsifier can be used including forexample, emulsifying wax, cetearyl alcohol, polysorbate 20, andceteareth 20, among others. In certain embodiments the tissue isincubated in lecithin overnight at 4° C. and washed with phosphatebuffered saline (PBS) three times (15 minutes per wash).

To remove DNA, the tissue can be treated with a DNA hydrolase including,for example, a DNase such as DNase I. Times and temperatures can bevaried according the type of enzyme and the amount of tissues beingprocessed. In one example, the tissue is incubated in a solution ofDNase I for 1 hour at room temperature and washed in PBS three times for15 minutes at room temperature.

Depending on the intended use of the scaffold, the tissue can be washedin deionized water. In some embodiments the tissue is washed indeionized water three times for 15 minutes at room temperature

The ECM can be sterilized by any of a number of standard methods withoutloss of function. For example and without limitation, the material canbe sterilized by propylene oxide or ethylene oxide treatment, gammairradiation treatment (0.05 to 4 mRad), gas plasma sterilization,peracetic acid sterilization, or electron beam treatment. Treatment withglutaraldehyde results in sterilization as well as increasedcross-linking of the ECM. This treatment substantially alters thematerial such that it is slowly resorbed or not resorbed at all andincites a different type of host remodeling, which more closelyresembles scar tissue formation or encapsulation rather thanconstructive remodeling. If desired, cross-linking of the proteinmaterial within the ECM can also be induced with, for example andwithout limitation, carbodiimide isocyanate treatments, dehydrothermalmethods, and photooxidation methods. In one non-limiting embodiment, theECM is disinfected by overnight gamma irradiation treatment with a totalexposure of 2 mRad. The ECM-derived material may be further processed byoptional drying, desiccation, lyophilization, freeze drying, and/orglassification. The ECM-derived material optionally can be furtherdigested, for example and without limitation by hydration (if dried),acidification, enzymatic digests with, for example and withoutlimitation, trypsin or pepsin and neutralization.

The biodegradable elastomeric scaffold as described herein may take manydifferent forms. In one non-limiting embodiment, the scaffold issubstantially planar (having much greater dimension in two dimensionsand a substantially smaller dimension in a third, comparable tobandages, gauze, and other substantially flexible, flat items). Inanother non-limiting embodiment, the biodegradable elastomeric scaffoldcomprises a non-woven fibrous article formed by electrodeposition of asuspension containing the synthetic polymeric component and thebiological polymeric component. In yet another non-limiting embodiment,the biodegradable elastomeric scaffold comprises a porous compositeformed by thermally induced phase separation. The biodegradableelastomeric scaffold can also have three-dimensional shapes useful fortreating wounds and tissue deficiencies, such as plugs, rings, wires,cylinders, tubes, or disks.

The biodegradable elastomeric scaffolds may be porous. Porosity may beaccomplished by a variety of methods. Although the biodegradableelastomeric scaffolds may be porous or non-porous, it is oftenadvantageous to use a process that produces a porous elastomericscaffold. Non-limiting examples of such processes include solventcasting/salt leaching, electrodeposition, and thermally induced phaseseparation. In other examples, porosity may be accomplished by creatinga mesh of fibers, such as by the aforementioned electrodeposition or byany suitable method of producing a woven or non-woven fiber matrix. Asused herein, the term “porosity” refers to a ratio between a volume ofall the pores within the polymer composition and a volume of the wholepolymer composition. For instance, a polymer composition with porosityof 85% would have 85% of its volume containing pores and 15% of itsvolume containing the polymer. In certain non-limiting embodiments, theporosity of the scaffold is at least 60%, 65%, 70%, 75%, 80%, 85%, or90%, or increments therebetween. In another non-limiting embodiment, theaverage pore size of the scaffold is between 0.1 and 300 microns,including increments therebetween. For example and without limitation, abiodegradable elastomeric scaffold that acts as a barrier to bacteriaand other pathogens may have an average pore size of less than 0.5microns or less than 0.2 microns. When the scaffold is to bemanufactured by electrodeposition, it is often advantageous to adjustthe pore size or degree of porosity by varying the polymer concentrationof the electrodeposition solution or by varying the spinning distancefrom the nozzle to the target. For example and without limitation, theaverage pore size may be increased by increasing the amount of polymericcomponents within the suspension used for electrodeposition, whichresults in larger fiber diameters and therefore larger pore sizes. Inanother non-limiting example, the average pore size can be increased byincreasing spinning distance from the nozzle to the target, whichresults in less adherence between fibers and a looser matrix.

In certain non-limiting embodiments, the biodegradable elastomericscaffold is made by using solvent casting and salt leaching. This methodinvolves dissolving the polymeric components that constitute thescaffold into a suitable organic solvent and then casting the solutioninto a mold containing small particles of predetermined size (known asporogens). Examples of suitable porogens include inorganic salts,crystals of saccharose, gelatin spheres or paraffin spheres. Byadjusting the porogen size and/or the ratio of porogen to solvent, theporosity of the final elastomeric scaffold may be adjusted. Aftercasting, the solvent is evaporated, and the resulting polymercomposition is immersed into a second solvent that dissolves theporogen, but not the polymer, to produce a porous, sheet-like structure.

In other non-limiting embodiments, electrodeposition is used tofabricate the elastomeric scaffold. The process of electrodepositioninvolves placing a polymer-containing fluid (for example, a polymersolution, a polymer suspension, or a polymer melt) in a reservoirequipped with a small orifice, such as a needle or pipette tip and ametering pump. One electrode of a high voltage source is also placed inelectrical contact with the polymer-containing fluid or orifice, whilethe other electrode is placed in electrical contact with a target(typically a collector screen or rotating mandrel). Duringelectrodeposition, the polymer-containing fluid is charged by theapplication of high voltage to the solution or orifice (for example,about 3-15 kV) and then forced through the small orifice by the meteringpump that provides steady flow. While the polymer-containing fluid atthe orifice normally would have a hemispherical shape due to surfacetension, the application of the high voltage causes the otherwisehemispherically shaped polymer-containing fluid at the orifice toelongate to form a conical shape known as a Taylor cone. Withsufficiently high voltage applied to the polymer-containing fluid and/ororifice, the repulsive electrostatic force of the chargedpolymer-containing fluid overcomes the surface tension and a charged jetof fluid is ejected from the tip of the Taylor cone and acceleratedtowards the target, which typically is biased between −2 to −10 kV.Optionally, a focusing ring with an applied bias (for example, 1-10 kV)can be used to direct the trajectory of the charged jet ofpolymer-containing fluid. As the charged jet of fluid travels towardsthe biased target, it undergoes a complicated whipping and bendingmotion. If the fluid is a polymer solution or suspension, the solventtypically evaporates during mid-flight, leaving behind a polymer fiberon the biased target. If the fluid is a polymer melt, the molten polymercools and solidifies in mid-flight and is collected as a polymer fiberon the biased target. As the polymer fibers accumulate on the biasedtarget, a non-woven, porous mesh is formed on the biased target.

The properties of the electrodeposited elastomeric scaffolds can betailored by varying the electrodeposition conditions. For example, whenthe biased target is relatively close to the orifice, the resultingelectrodeposited mesh tends to contain unevenly thick fibers, such thatsome areas of the fiber have a “bead-like” appearance. However, as thebiased target is moved further away from the orifice, the fibers of thenon-woven mesh tend to be more uniform in thickness. Moreover, thebiased target can be moved relative to the orifice. In certainnon-limiting embodiments, the biased target is moved back and forth in aregular, periodic fashion, such that fibers of the non-woven mesh aresubstantially parallel to each other. When this is the case, theresulting non-woven mesh may have a higher resistance to strain in thedirection parallel to the fibers, compared to the directionperpendicular to the fibers. In other non-limiting embodiments, thebiased target is moved randomly relative to the orifice, so that theresistance to strain in the plane of the non-woven mesh is isotropic.The properties of the electrodeposited elastomeric scaffold may also bevaried by changing the magnitude of the voltages applied to theelectrodeposition system. In one non-limiting embodiment, theelectrodeposition apparatus includes an orifice biased to 12 kV, atarget biased to −7 kV, and a focusing ring biased to 3 kV. Moreover, auseful orifice diameter is 0.047″ (I.D.) and a useful target distance isabout 23 cm. Other electrodeposition conditions that can be variedinclude, for example and without limitation, the feed rate of thepolymer solutions, the solution concentrations, and the polymermolecular weight. Non-limiting examples of useful range of high-voltageto be applied to the polymer suspension is from 0.5 to 30 kV, from 5 to25 kV, and from 10 to 15 kV.

In another non-limiting embodiment, thermally induced phase separation(TIPS) is used to fabricate the biodegradable elastomeric scaffold. Thismethod involves dispersing the polymeric components in a solvent (forexample and without limitation, DMSO—dimethyl sulfoxide) and thencasting, for example by injecting or otherwise placing the compositioninto a mold. The mold can have any useful shape, such as a sheet or net.In a typical TIPS fabrication process, a pre-formed mold is cooled tolow temperature (for example and without limitation −80° C.), whichcauses the polymeric components to separate out of the solvent. The moldis then transferred to ethanol to extract the DMSO.

Fabrication and modification of the biodegradable elastomeric scaffoldcan comprise multiple steps using multiple techniques using polymercompositions that are the same or different. In one non-limitingexample, TIPS is used to fabricate the biodegradable elastomericscaffold and electrodeposition is used to form a fiber coating onto oraround the scaffold. In another non-limiting example, solventcasting/salt leaching is used to fabricate the biodegradable elastomericscaffold and electrodeposition is used to form a fiber coating onto oraround the scaffold. The electrodeposition solution can contain one ormore of any polymeric components, including synthetic polymericcomponents, biological polymeric components, or mixtures of both. Thefiber coating formed by electrodeposition can be coated onto or aroundthe entire scaffold or portions of the scaffold.

After fabricating the biodegradable elastomeric scaffold, the planar orthree-dimensional surface of the scaffold may be functionally modified(functionalized) for any purpose, such as, without limitation, topromote cellular adhesion and migration onto and/or into the scaffold.In one non-limiting example, the surface is first treated to introduce areactive group on the surface by any useful process, such as one of themany processes known in the art. Second, the activated surface isreacted with an adhesion-promoting peptide or group. The reactive groupon the surface can be, for example and without limitation, a hydroxylgroup or an amine group. In one embodiment, radio-frequency glowdischarge is used to produce plasma containing ammonia gas and aminegroups are introduced to the surface by treatment with the plasma. Inanother embodiment, radio-frequency glow discharge is used to introducehydroxyl groups to the surface by treatment with plasma.

The activated surface can be modified with an adhesion-promotingoligopeptide to promote cellular ingrowth into and/or onto the scaffold.Non-limiting examples of adhesion-promoting oligopeptides include: RGDor RGDS (SEQ ID NO.: 1), a recognition site for fibronectin,vitronectin, fibrinogen, von Willebrand factor, and collagen; LDV, REDV(SEQ ID NO.: 2), PHSRN (SEQ ID NO.: 3), and KNEED (SEQ ID NO.: 4), whichare recognition sites for fibronectin; YIGSR (SEQ ID NO.: 5) and IKVAV(SEQ ID NO.: 6), which are recognition sites for laminin; and DGEA (SEQID NO.: 7), a recognition site for collagen.

In one specific non-limiting embodiment, the scaffold is functionalizedto present the peptide RGDS (SEQ ID NO.: 1) on its surface. First, thesurface is treated with radio-frequency glow discharge containingammonia gas to introduce amine groups. Ammonia-containing gas isgenerated by connecting a flask containing ammonium hydroxide (30 wt %solution) to the glow discharge reactor and maintaining pressure at3×10⁻³ Torr. The surface is further treated with 1,4-diisocyanatobutaneto provide a reactive isocyanate group. Next, RGDS (SEQ ID NO.: 1) isattached to the activated surface. The activated surface is immersed ina solution of 20 μg/mL RGDS (SEQ ID NO.: 1) in PBS for 10 hours and thenrinsed with PBS.

One or more of therapeutic agents can be introduced into thebiodegradable elastomeric scaffold by any useful method, such as,without limitation absorption, adsorption, deposition, admixture with apolymer composition used to manufacture the scaffold and linkage of theagent to a component of the scaffold. In one non-limiting example, thetherapeutic agent is introduced into a backbone of a polymer used in thescaffold. By adding the therapeutic agent to the elastomeric polymeritself, the rate of release of the therapeutic agent may be controlledby the rate of polymer degradation. In another non-limiting example, thetherapeutic agent is introduced when the scaffold is being made. Forinstance, during a solvent casting or TIPS process, the therapeuticagent can be added to the solvent with the polymer in the pre-formedmold. During an electrodeposition process, the therapeutic agent can beelectrosprayed onto the polymer being spun. In yet another non-limitingexample, the therapeutic agent is introduced into the scaffold after thepatch is made. For instance, the scaffold may be “loaded” withtherapeutic agent(s) by using static methods. For instance, the scaffoldcan be immersed into a solution containing the therapeutic agent,permitting the agent to absorb into and/or adsorb onto the scaffold. Thescaffold may also be loaded by using dynamic methods. For instance, asolution containing the therapeutic agent can be perfused orelectrodeposited into the scaffold. In another instance, a therapeuticagent can be added to the biodegradable elastomeric scaffold before itis implanted in the patient.

Therapeutic agents within the biodegradable elastomeric scaffold can beused in any number of ways. In one non-limiting embodiment, atherapeutic agent is released from the scaffold. For example and withoutlimitation, anti-inflammatory drugs are released from the scaffold todecrease an immune response. In another non-limiting embodiment, atherapeutic agent is intended to substantially remain within thescaffold. For example and without limitation, chemoattractants aremaintained within the scaffold to promote cellular migration and/orcellular infiltration into the scaffold.

In one non-limiting embodiment, the biodegradable elastomeric scaffoldsrelease therapeutic agents when the polymeric components degrade withinthe patient's body. For example and without limitation, the individualbuilding blocks of the polymers may be chosen such that the buildingblocks themselves provide a therapeutic benefit when released in situthrough the degradation process. In one non-limiting embodiment, one ofthe polymer building blocks is putrescine, which has been implicated asa substance that causes cell growth and cell differentiation.

In another non-limiting embodiment, at least one therapeutic agent isadded to the biodegradable elastomeric scaffold before it is implantedin the patient. Generally, the therapeutic agents include any substancethat can be coated on, embedded into, absorbed into, adsorbed onto, orotherwise attached to or incorporated onto or into the biodegradableelastomeric scaffold that would provide a therapeutic benefit to apatient. Non-limiting examples of such therapeutic agents includeantimicrobial agents, growth factors, emollients, retinoids, and topicalsteroids. Each therapeutic agent may be used alone or in combinationwith other therapeutic agents. For example and without limitation, abiodegradable elastomeric scaffold comprising neurotrophic agents orcells that express neurotrophic agents may be applied to a wound that isnear a critical region of the central nervous system, such as the spine.Alternatively, the therapeutic agent may be blended with the polymerwhile the polymer is being processed. For example, the therapeutic agentmay be dissolved in a solvent (e.g., DMSO) and added to the polymerblend during processing. In another embodiment, the therapeutic agent ismixed with a carrier polymer (e.g., polylactic-glycolic acidmicroparticles) which is subsequently processed with an elastomericpolymer. By blending the therapeutic agent with a carrier polymer orelastomeric polymer itself, the rate of release of the therapeutic agentmay be controlled by the rate of polymer degradation.

In certain non-limiting embodiments, the therapeutic agent is a growthfactor, such as a neurotrophic or angiogenic factor, which optionallymay be prepared using recombinant techniques. Non-limiting examples ofgrowth factors include basic fibroblast growth factor (bFGF), acidicfibroblast growth factor (aFGF), vascular endothelial growth factor(VEGF), hepatocyte growth factor (HGF), insulin-like growth factors 1and 2 (IGF-1 and IGF-2), platelet derived growth factor (PDGF), stromalderived factor 1 alpha (SDF-1 alpha), nerve growth factor (NGF), ciliaryneurotrophic factor (CNTF), neurotrophin-3, neurotrophin-4,neurotrophin-5, pleiotrophin protein (neurite growth-promoting factor1), midkine protein (neurite growth-promoting factor 2), brain-derivedneurotrophic factor (BDNF), tumor angiogenesis factor (TAF),corticotrophin releasing factor (CRF), transforming growth factors□ αand β (TGF-α and TGF-β), interleukin-8 (IL-8), granulocyte-macrophagecolony stimulating factor (GM-CSF), interleukins, and interferons.Commercial preparations of various growth factors, includingneurotrophic and angiogenic factors, are available from R & D Systems,Minneapolis, Minn.; Biovision, Inc, Mountain View, Calif.; ProSpec-TanyTechnoGene Ltd., Rehovot, Israel; and Cell Sciences®, Canton, Mass.

Methods of promoting wound healing or tissue generation or regenerationin a patient also are provided. The methods comprise, withoutlimitation, implanting an elastomeric scaffold as described herein at ornear a site for wound healing or tissue generation or regeneration inthe patient. In any such method, the elastomeric scaffold may comprise atherapeutic agent as described herein.

In certain non-limiting embodiments, the therapeutic agent is anantimicrobial agent, such as, without limitation, isoniazid, ethambutol,pyrazinamide, streptomycin, clofazimine, rifabutin, fluoroquinolones,ofloxacin, sparfloxacin, rifampin, azithromycin, clarithromycin,dapsone, tetracycline, erythromycin, ciprofloxacin, doxycycline,ampicillin, amphotericin B, ketoconazole, fluconazole, pyrimethamine,sulfadiazine, clindamycin, lincomycin, pentamidine, atovaquone,paromomycin, diclazaril, acyclovir, trifluorouridine, foscarnet,penicillin, gentamicin, ganciclovir, iatroconazole, miconazole,Zn-pyrithione, and silver salts such as chloride, bromide, iodide andperiodate.

In certain non-limiting embodiments, the therapeutic agent is ananti-inflammatory agent, such as, without limitation, a NSAID, such assalicylic acid, indomethacin, sodium indomethacin trihydrate,salicylamide, naproxen, colchicine, fenoprofen, sulindac, diflunisal,diclofenac, indoprofen, sodium salicylamide; an anti-inflammatorycytokine; an anti-inflammatory protein; a steroidal anti-inflammatoryagent; or an anti-clotting agents, such as heparin. Other drugs that maypromote wound healing and/or tissue regeneration may also be included.

In certain non-limiting embodiments, the therapeutic agent comprisescells that are added to the biodegradable elastomeric scaffold before orat the time of implantation. In such embodiments, it is oftenadvantageous to use a porous biodegradable elastomeric scaffold, so thatthe cells may be incorporated into the porous structure of the scaffold(a condition referred to as “microintegration”). In this way, most ofthe cells will have a tendency to be trapped or otherwise containedwithin the porous structure of the scaffold. The cells that aremicrointegrated may remain after the biodegradable elastomeric scaffoldhas fully disintegrated within the patient. However, the microintegratedcells may also be merely cells that act as precursors to the finaltissue that is formed when the biodegradable elastomeric scaffold hasfully degraded.

Cells may be autologous (obtained from the patient to receive thescaffold), from an allogeneic or xenogeneic source or from any usefulcell line, such as, without limitation, stem cells that are capable ofcellular growth, remodeling, and/or differentiation. By way of exampleonly, the cells that may be incorporated onto or into the biodegradablescaffold include stem cells, precursor cells, smooth muscle cells,skeletal myoblasts, myocardial cells, endothelial cells, and geneticallymodified cells. Various commercially available cell lines includeClonetics® Primary Cell Systems (Lonza Group, Inc., Switzerland), ATCC.

Cells may be microintegrated with the biodegradable elastomeric scaffoldusing a variety of methods. For example and without limitation, theelastomeric scaffold may be placed in a suitable growth medium for thecells of interest, and then exposed to the cells. The cells are allowedto proliferate on the surface and interstices of the elastomericscaffold. The elastomeric scaffold is then removed from the growthmedium, washed if necessary, and implanted. Alternatively, the cells maybe placed in a suitable buffer or liquid growth medium and drawn throughthe scaffold by using vacuum filtration. In another non-limitingembodiment, the cells of interest are dissolved into an appropriatesolution (e.g., a growth medium or buffer) and then sprayed onto abiodegradable elastomeric scaffold while the scaffold is being formed byelectrodeposition. In yet another non-limiting embodiment, the cells areplaced in a solution that is biased and then electrosprayed onto thebiodegradable elastomeric scaffold while it is being electrodeposited.By way of example only, the cells that may be incorporated on or intothe biodegradable scaffold include chondrocytes, stem cells, precursorcells, smooth muscle cells, skeletal myoblasts, myocardial cells,endothelial cells, and genetically modified cells.

In one non-limiting embodiment, the genetically modified cells arecapable of expressing a therapeutic substance, such as a growth factor.Cells can be modified by any useful method in the art. For example andwithout limitation, the therapeutic agent is a growth factor that isreleased by cells transfected with cDNA encoding for the growth factor.Therapeutic agents that can be released from cells include, withoutlimitation, a neurotrophic factor, such as nerve growth factor,brain-derived neurotrophic factor, neurotrophin-3, neurotrophin-4,neurotrophin-5, and ciliary neurotrophic factor; a growth factor, suchas basic fibroblast growth factor (bFGF), acidic fibroblast growthfactor (aFGF), vascular endothelial growth factor (VEGF), hepatocytegrowth factor (HGF), insulin-like growth factors (IGF), platelet derivedgrowth factor (PDGF), transforming growth factor-beta (TGF-β),pleiotrophin protein (neurite growth-promoting factor 1), and midkineprotein (neurite growth-promoting factor 2); an anti-inflammatorycytokine; and an anti-inflammatory protein. The cells may be autologous,allogeneic, etc.

In addition to providing biodegradable elastomeric scaffolds asdescribed above, methods of using such elastomeric scaffolds areencompassed herein. Generally, a biodegradable elastomeric scaffold canbe implanted by using any suitable medical procedure that facilitatesuse of the scaffold to provide a therapeutic benefit. As used herein,the terms “implanted” and “implantation” and like terms refer to an actof delivering a biodegradable elastomeric scaffold to a site within thepatient. The site of implantation in a patient typically is “at or neara site for wound healing or tissue generation or regeneration in thepatient,” meaning the scaffold-containing device is implanted in, on,onto, adjacent to or in proximity to a desired site of delivery tofacilitate healing and/or tissue generation or regeneration to repair aninjury or defect in the patient and/or to achieve a desired effect inthe patient, such as wound drainage. The delivery method may alsoinclude minimally invasive methods such as by catheter based technologyor by needle injection. The patient may be human or animal. The scaffoldmay be delivered by any surgical procedure, including minimally invasivetechniques, such as laparoscopic surgery, as well as invasive techniquessuch as thoracic surgery and fasciotomy. In certain non-limitingembodiments, the elastomeric scaffolds are used as surgical fabrics. Thebiodegradable elastomeric scaffold may be implanted alone or implantedin conjunction with surgical fasteners, such as sutures, staples,adhesives, screws, pins, and the like. Additionally, biocompatibleadhesives, such as, without limitation, fibrin-based glue may be used tofasten the elastomeric scaffolds as well.

In yet another non-limiting embodiment, the scaffold can be in the formof a powder or fine particles (for example, formed by shredding anon-woven mesh formed by electrodeposition or TIPS). In thesesituations, it may be advantageous to derivatize the elastomericscaffold with therapeutic agents, such as antibiotics or growth factors,prior to insertion into the wound.

EXAMPLES Example 1 Manufacturing Acellular Spinal Cord and Dura MaterBiological Scaffolds

In one example, porcine spinal cord was obtained. Using forceps,scissors and a scalpel, dura mater was removed from the spinal cord. Theinner dura mater surface was scrapped with scalpel blade to remove anydebris. The spinal cord and dura were placed in separate containers andtreated in the same manner as listed below. The spinal cord was cuteither longitudinally or in cross-section (to increase surface area) andplaced in a cassette (e.g., safety container to protect 3-D structure ofcord throughout process). Optionally tissue was enzymatically treatedusing trypsin-EDTA for 30 minutes at 37° C. The tissue was incubated inTRITON X-100™ (4-octylphenol polyethoxylate) solutions at 3% for periodsup to 2-3 days at 4° C. This step was repeated with a solution of TritonX-100™ at 6% and again with a solution of Triton X-100™ at 9%. Thespinal cord tissue was incubated in lecithin or lecithin-deoxycholate toremove lipids overnight at 4° C. Dura mater was not subjected to thisprocedure. Tissue was then washed in TRITON X100™ 3% or SDS 1% for 1-2hours. The tissue was rinsed in PBS×3 for 15 minutes at roomtemperature. Then the tissue was incubated in a solution of DNase I for1 hour at room temperature. The tissue was washed in PBS three times for15 minutes at room temperature. Lastly, the tissue was washed indeionized water three times for 15 minutes at room temperature. Theprocedure produced a gel-like acellular spinal cord material, and asheet of acellular dura mater material. Sections of each material weresent for histology to confirm lack of cells. Biocompatibility was testedby culturing the scaffolds with either primary neuronal cells or aneuronal cell line (e.g. PC 12 cell line)

Example 2 Characterization of the Neuronal Scaffolds

Described in this example is the characterization of the neuronalscaffold. After the last step of the process described in the Example 1,the acellular spinal cord parenchyma-derived neuronal scaffold isgel-like. FIG. 1 is a digital image showing the gel-like quality of thescaffold. The thick arrow indicates the gel-like substance and the thinarrow indicates the pia matter.

After forming the neuronal scaffold, the scaffold is acellular. Variousmethods were used to determine whether the scaffold was acellular.First, fluorescent stains, such as DAPI (4′,6-diamidino-2-phenlindole),were used to determine whether cells are present. FIGS. 2A-2B and FIG.8A are fluorescence photomicrographs of the scaffold stained with DAPI,where lack of fluorescence correlated with lack of nuclei and cellswithin the scaffold. Second, histological stains, such as Masson'strichrome, were also be used. FIG. 3 and FIG. 8B show photomicrographsof Masson's trichrome stained scaffold, which showed that cells are notpresent within the scaffold. FIGS. 4A-4D provide comparisons between theacellular spinal cord parenchyma-derived neuronal scaffolds and nativeadult porcine spinal cord. FIGS. 4A-4B show acellular porcine spinalcord parenchyma-derived neuronal scaffold that has been stained withhematoxylin and eosin (FIG. 4A) or with Masson's trichrome (FIG. 4B).FIGS. 4C-4D show Masson's trichrome stained grey matter (FIG. 4C) andwhite matter (FIG. 4D) of a normal adult porcine spinal cord.

The porosity, topology, and morphology of the scaffold were determinedby various methods, including scanning electron microscopy (SEM).Specifically, samples were fixed in 2.5% glutaraldehyde in PBSovernight, rinsed with PBS, 15 min at RT and treated with 1% Osmiumtetroxide in PBS for 60 minutes at room temperature. The tissue wasrinsed again in PBS and processed with sequential ethanol dehydration:30%, 50%, 70%, 90% for 15 minutes each; 100%×15 min.×3. The sample wastreated with HMDS (hexamethyldisiazane) for 1 hour at room temperature,removed from HMDS and air-dried overnight. Samples were then sputtercoated and scanned. FIGS. 5A-5B are scanning electron micrographs ofacellular spinal cord parenchyma-derived neuronal scaffold at 600×magnification (FIG. 5A) and at 2,000× magnification (FIG. 5B).

Example 3 Testing for Biocompatibility of the Neuronal Scaffolds

Biocompatibility of the neuronal scaffold was tested by culturingprimary neuronal cells and neuronal cell lines on the scaffold. Ratadrenal pheochromocytoma (PC12) cells were obtained from ATCC (AmericanType Culture Collection, Manassas, Va.), ATCC catalog number CRL-1721.The PC12 cells were grown in DMEM with 10% heat-inactivated horse serum,5% fetal bovine serum, 1% penicillin-streptomycin solution (stocksolution: 10,000 units penicillin and 10,000 μg streptomycin/ml) in ahumidified incubator at 37° C. supplemented with 5% CO₂ in plastic cellculture-treated flasks. Cells were not allowed to become more than 50%confluent in culture flasks before sub-culturing. Prior to seeding onneural scaffolds, adherent PC-12 cells were trypsinized (5 ml 0.25%trypsin with EDTA/75 sq. cm flask) to release and remove cells fromculture flasks. Once cells were non-adherent, the trypsin wasneutralized with 20 ml culture medium (containing horse serum and fetalbovine serum). Cells were then centrifuged at 800 g for 5 minutes andthe supernatant was removed. Cells were resuspended in 3 ml culturemedium and counted using a hemocytometer. A total of 1.5×10⁶ cells wereseeded on each scaffold (approximately 5×10⁵/square centimeter). Cellswere allowed to grow on neural scaffolds for 2 days. The neuralscaffold-PC12 biomaterials were fixed in 10% (neutral buffered) formalinfor 24 hours, mounted in paraffin, sectioned (5 μm sections), mounted onglass slides, stained (H&E, Masson's trichrome) and coverslipped. Thesecultures were not supplemented with NGF (typically 50 ng/ml), but itcould be added to this cell line to stimulate neuron phenotype includingneurite outgrowth.

The response of the PC12 cells to the neuronal scaffolds was determinedby Masson's trichrome stain. FIGS. 6A-6C and 7A-7B showsphotomicrographs of Masson's trichrome stained acellular spinal cordparenchyma-derived neural scaffold implanted with neuronal cells (PC12).FIGS. 6A-6C show neuronal cell growth and migration into the scaffold,where neuronal cells (red, thin arrows) grew on and into the scaffold(blue, thick arrows). FIGS. 7A-7B show neuronal cell growth andmigration in this scaffold (blue, thick arrows). Neuronal cells grew onthe surface of the scaffold (red, thin arrows) and migrated into thescaffold (arrowheads). FIGS. 8C-8D show neuronal cells (red) growing onthe surface of dura mater-derived neural scaffold (blue).

Having described this invention, it will be understood to those ofordinary skill in the art that the same can be performed within a wideand equivalent range of conditions, formulations and other parameterswithout affecting the scope of the invention or any embodiment thereof.

Having now described the features, discoveries and principles of theinvention, the manner in which the neural scaffolds are used andinstalled, the characteristics of the construction, arrangement andmethod steps, and the advantageous, new and useful results obtained; thenew and useful structures, devices, elements, arrangements, process,parts and combinations are set forth in the appended claims.

The invention claimed is:
 1. A method of manufacturing a neural scaffoldconsisting essentially of: isolating central nervous system tissueconsisting essentially of dura mater; enzymatically digesting thecentral nervous system tissue in a solution of trypsin-EDTA; incubatingthe tissue in a solution comprising a non-ionic surfactant; washing thetissue to remove the non-ionic surfactant; incubating the tissue in asolution comprising DNase; and washing the tissue to remove the DNase,wherein the method does not include use of another emulsifier.
 2. Themethod of claim 1, wherein the tissue is enzymatically digested for 30minutes at 37° C.
 3. The method of claim 1, wherein the surfactant is4-octylphenol polyethoxylate.
 4. The method of claim 3, wherein thetissue is incubated for a first period of greater than forty eight hoursin a first concentration of 4-octylphenol polyethoxylate.
 5. The methodof claim 4, wherein the first concentration of 4-octylphenolpolyethoxylate is 3% by volume.
 6. The method of claim 4, where thetissue is incubated for a second period of greater than forty eighthours in a second concentration of 4-octylphenol polyethoxylate.
 7. Themethod of claim 6, wherein the second concentration of 4-octylphenolpolyethoxylate is 6% by volume.
 8. The method of claim 6, where thetissue is incubated for a third period of greater than forty eight hoursin a third concentration of 4-octylphenol polyethoxylate.
 9. The methodof claim 8, wherein the third concentration of 4-octylphenolpolyethoxylate is 9% by volume.
 10. The method of claim 1, wherein thecentral nervous system is spinal cord tissue.
 11. The method of claim 1,wherein the tissue is incubated in DNase for at least one hour at roomtemperature.
 12. The method of claim 11, wherein the tissue is washed inphosphate buffered saline after incubating in DNase.
 13. The method ofclaim 12, wherein the tissue is washed in de-ionized water after beingwashed in phosphate buffered saline.
 14. The method of claim 1, furthercomprising adding a therapeutic agent to the tissue.
 15. A method ofmanufacturing a neural scaffold consisting of: isolating central nervoussystem tissue comprising dura mater; enzymatically digesting the centralnervous system tissue in a solution of trypsin-EDTA; incubating thetissue in a solution comprising a non-ionic surfactant; washing thetissue to remove the non-ionic surfactant; incubating the tissue in asolution comprising DNase; and washing the tissue to remove the DNase.16. A method of manufacturing a neural scaffold comprising: isolatingcentral nervous system tissue comprising dura mater; enzymaticallydigesting the central nervous system tissue in a solution oftrypsin-EDTA; incubating the tissue in a solution comprising a non-ionicsurfactant; washing the tissue to remove the non-ionic surfactant;incubating the tissue in a solution comprising DNase; and washing thetissue to remove the DNase, wherein the method does not include the useof another emulsifier.